Would changing the differential fluid to a full synthetic oil increase MPG at all or would it be about the same as regular fluid?

kevin

 

Not gonna help MPG but a good idea. Our dealership uses synthetic on all diff service, whether you want it or not.

 

Actually, if you've got some miles on your truck (and by 'some', I mean above 30K), you probably would notice a little bit of an increase if the fluid has never been changed. Old gear oil is like trying to stir frozen syrup... hence it's taking a little more effort to get your truck going. Overall though, synthetic would probably be a good idea anyway. As much stress as the rear-end is under, I would think having sythetic in there would be nothing but beneficial.

 

I picked up approximately 1 mpg on both vehicles thanks to synthetic gear lube. The advantage of my gear lube of choice is that it's lifetime fill. I never had to change it.


Bill,

 

I understand the 9-1/4 rear end hold just under 3 quarts. I was able to pump out 2 quarts (with a little hand pump I use to fill my outboads lower unit). I didn't want to deal with removing the pumpkin and having to make a gasket out of RTV sealant.
So now that I need to replace 2 quarts (must still be 1 quart that i couldn't remove) can i mix the existing 1 quart with 2 quarts of synthetic, or synthetic blend or just use the 75w90 petroleum base?

 

Pull off the cover and do it right. go get a new gasket when you re-install the cover. You have a dodge, don't be cheep and take shortcuts, the gasket can't be more than $5-$10...

 

Where is that Ram pride! Do it right the first time.

 

Looks like I'm going to answer my own question, here is what I found at two different Oil Co websites:
Castrol SYNTEC BLEND provides an added level of synthetic protection against the stress these conditions place on an engine.
Question: Wouldn't it be better (or just as good) if I mixed Syntec with GTX?
Answer: Although all the oils are compatible, this is not the way we make Syntec Blend - it is fully formulated in its own right with conventional GTX base stocks and Syntec molecular components to achieve its unique properties.

SEAL AND LUBRICANT COMPATIBILITY
Red Line Gear Oils are designed to be compatible with
seals which were designed for use with petroleum products.
Reduced temperatures and improved deposit control
should allow longer seal life. Red Line Gear Oils are
compatible with petroleum and most other synthetics,
so flushing is not required.
I added two quarts of Coastal Unilube 75w90 synthetic blend, their bottles also said "compatable", I've only put 10 miles on, but i gave it the finger in the hole check, and it seems to have blended ok.
Any real life experience out there? let me know, thanks Bill